Method and apparatus for cleaning a CVD chamber

ABSTRACT

The present invention is a method and apparatus for cleaning a chemical vapor deposition (CVD) chamber using cleaning gas energized to a plasma in a gas mixing volume separated by an electrode from a reaction volume of the chamber. In one embodiment, a source of RF power is coupled to a lid of the chamber, while a switch is used to couple a showerhead to ground terminals or the source of RF power.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to semiconductor substrateprocessing systems. More specifically, the present invention relates tomethods and apparatus for performing deposition processes insemiconductor substrate processing systems.

2. Description of the Related Art

In the fabrication of integrated circuits, deposition processes such aschemical vapor deposition (CVD) or plasma enhanced CVD processes areused to deposit films of various materials upon semiconductorsubstrates. Herein such processes are collectively referred to as CVDprocesses. During a CVD process, chemical reactions used for depositinga desired material take place in an enclosed process chamber. When thematerial is deposited on the substrate, residue comprising thismaterial, as well as by-products of the CVD process, accumulates on theinternal walls and other components of the process chamber. The residuebuilds up, as more substrates are processed in the chamber, and leads togeneration of particles and other contaminants and, as such, todegradation of the deposited films. Consequently, it is recommended toclean the interior of the CVD chamber on a regular basis.

When chamber cleaning is performed, production of the integratedcircuits is temporarily interrupted. As a result, productivity of theCVD process, as measured by substrate throughput, decreases. In order toincrease the productivity, it is necessary to facilitate a cleaningprocess that increases a number of substrates that may be processedbefore a need in chamber cleaning arises, as well as to decrease theduration of the cleaning process.

Generally, two types of methods are used to clean the CVD chambers. Bothmethods use a cleaning gas (e.g., fluorine (F) based gas) to removepost-CVD residue from the interior of the chamber and may be performedwithout opening the chamber, i.e., in situ.

In the first cleaning method, the cleaning gas is energized to a plasmawithin a remote plasma source that forms and releases into the CVDchamber free radicals and ionic species of the cleaning gas. In the CVDchamber, the radicals and ionic species chemically react with theresidue and transform the residue into volatile compounds. The volatilecompounds are then evacuated from the chamber. One such method isdisclosed in commonly assigned U.S. patent application Ser. No.10/122,481, filed Apr. 12, 2002, which is incorporated herein byreference.

In the cleaning second method, the cleaning gas is energized to theplasma inside the CVD chamber using a radio-frequency (RF) plasma sourceand, as such, the free radicals and ionic species of the cleaning gascan attack the residue and internal parts of the chamber both chemicallyand physically.

In the prior art, the free radicals and ionic species of the cleaningplasma readily recombine within the CVD chamber during a cleaningprocedure. Recombination of the free radicals and ionic species resultsin formation of reactive species that may chemically react with thematerial (e.g., aluminum (Al), stainless steel, and the like) ofcomponents of the CVD chamber, e.g., a gas distribution plate, asusceptor (substrate pedestal), a substrate heater, a protective lining,and the like. During the cleaning process, such chemical reactions, aswell as physical bombardment (e.g., an ionic bombardment) of theinternal parts, may cause damage to the CVD chamber. Further, in manyapplications, these chemical reactions can produce non-volatileresidue-like deposits (e.g., aluminum fluoride (AlF₃)), which also maycontaminate the substrates during the following CVD processing of thesubstrates.

Therefore, there is a need in the art for a method and apparatus forcleaning a CVD chamber with minimal damage to the internal parts.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for cleaning a chemicalvapor deposition (CVD) chamber with minimal damage to the internalparts. The method uses cleaning gas energized to RF plasma in a volumeseparated by an electrode from a reaction volume of the chamber. In oneembodiment, a source of RF power is coupled to a lid of the chamber,while a switch is used to couple a gas distribution plate to groundterminals or the source of RF power.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 depicts a schematic diagram of a plasma processing apparatus inaccordance with the present invention;

FIG. 2 depicts a flow diagram of a cleaning process in accordance withone embodiment of the present invention; and

FIG. 3 is a table summarizing the processing parameters of oneembodiment of the present invention when practiced using the apparatusof FIG. 1.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

The present invention is a method and apparatus for plasma cleaning,with minimal damage to the internal parts, a process chamber of achemical vapor deposition (CVD) reactor or a plasma enhanced CVD (PECVD)reactor. Herein either reactor is referred to as a CVD reactor.

FIG. 1 depicts a schematic diagram of an exemplary CVD reactor 100,which may be used to perform a cleaning process in accordance with thepresent invention. The images in FIG. 1 are simplified for illustrativepurposes and are not depicted to scale. An example of the CVD reactorthat may used to perform the invention is the PRODUCER® Reactor,available from Applied Materials, Inc. of Santa Clara, Calif. ThePRODUCER® Reactor is disclosed in commonly assigned U.S. Pat. No.5,855,681, issued Jan. 5, 1999, which is incorporated herein byreference. The PRODUCER® Reactor comprises a CVD chamber having twoisolated processing regions. Each of the processing regions may be usedto deposit dielectric and other materials. FIG. 1 depicts one processingregion as a process chamber 102.

Other CVD reactors and chambers may also be used to practice theinvention, e.g., the CVD chamber disclosed in commonly assigned U.S.Pat. No. 6,364,954 B2, issued Apr. 2, 2002, which is incorporated hereinby reference. This chamber is available from Applied Materials, Inc. ofSanta Clara, Calif. under the trademark DXZ®.

The reactor 100 comprises the process chamber 102, a source 131 ofradio-frequency (RF) power, a gas panel 108, a source 136 of backsidegas, a heater power supply 106, a vacuum pump 104, support systems 107,and a controller 110. In other embodiments, the reactor 100 may compriseat least one optional plasma magnetizing solenoid, an optional source ofsubstrate RF bias, and an optional remote plasma source (all not shown).

The process chamber 102 generally is a vacuum vessel, which comprises afirst portion 103 and a second portion 105. In one embodiment, the firstportion 103 is coupled to the vacuum pump 104 and comprises a substratepedestal 126, a protective lining 113, and a sidewall 158. The secondportion 105 is coupled to the gas panel 108 and comprises a lid 112. Thelid 112 further comprises an optional blocking plate 164 and a gasdistribution plate (showerhead) 120, which defines a gas mixing volume152 and a reaction volume 154.

In one embodiment, the lid 112, the blocking plate 164, and theshowerhead 120, as well as the sidewall 158, are formed from at leastone conductive material, such as metal (e.g., aluminum (Al) and thelike) or metal alloy (e.g., stainless steel and the like). Further, thesubstrate pedestal 126 and the protective lining 113 may be formed fromor comprise sub-components that are formed from the at least one of suchconductive materials. The referred to components of the process chamber102 may also comprise portions and/or sub-components formed fromnon-conductive materials (e.g., ceramic, polyimide, and the like) orfrom any combination of conductive and non-conductive materials. Assuch, scope of the present invention is not limited to the processchamber 102 having components formed entirely from conductive materials.

The substrate pedestal 126 is used to support a substrate 128 (e.g., 300mm silicon (Si) wafer) during a CVD process. In one embodiment, thesubstrate pedestal 126 comprises an embedded resistive heater 130 toheat the substrate pedestal. Alternatively, the substrate pedestal 126may comprise a source of radiant heat (not shown), such as gas-filledlamps and the like. An embedded temperature sensor 132, e.g., athermocouple, monitors, in a conventional manner, the temperature of thesubstrate pedestal 126. The measured temperature is used in a feedbackloop to regulate the output of the heater power supply 106 that iscoupled to the heater 130 or, alternatively, to the gas-filled lamps.

The support pedestal 126 further comprises a gas supply conduit 137,which provides gas, e.g., helium, from a source 136 to the backside ofthe wafer 128 through grooves (not shown) in the support surface of thepedestal. The gas facilitates heat exchange between the support pedestal126 and the wafer 128. Using the backside gas, the temperature of thewafer 128 may be controlled between about 200 and 800 degrees Celsius.

The gas panel 108 comprises process and cleaning gases, as well asequipment for regulating the flow of each gas. In one embodiment, aprocess gas (or gas mixture), as well as a cleaning gas, is deliveredfrom the gas panel 108 into the process chamber 102 through an inletport 160 disposed in the lid 112. Herein the terms “gas” and “gasmixture” are used interchangeably. The inlet port 160 is fluidlyconnected to a first plenum 162, where gases may diffuse radially acrossthe optional blocking plate 164, as indicated by arrows 167.Alternatively, the process gas and/or cleaning gas may by delivered intothe process chamber 102 through a separate inlet port (not shown) in thelid or showerhead.

The process or cleaning gas passes through apertures 168 in the blockingplate 164 and enters a second plenum 166 that is formed between theshowerhead 120 and the blocking plate 164. The showerhead 120 fluidlyconnects the second plenum 166 to the reaction volume 154 via aplurality of apertures 172. The showerhead 120 may comprise differentzones such that various gases can be released into the reaction volume154 at various flow rates.

The vacuum pump 104 is adapted to an exhaust port 186 formed in thesidewall 158 of the process chamber 102. The vacuum pump 104 is used tomaintain a desired gas pressure in the process chamber 102, as well asevacuate post-processing gases and other volatile compounds (i.e.,during a cleaning process discussed below) from the process chamber. Inone embodiment, the vacuum pump 104 comprises a throttle valve (notshown) to control gas conductance in a path between the pump and thechamber. Gas pressure in the process chamber 102 is monitored by apressure sensor 118. The measured value is used in a feedback loop tocontrol the gas pressure during processing the wafer 128 or during thecleaning process.

The source 131 comprises a RF generator 134 and an associated matchingnetwork 135. The generator 134 may generally be tuned in a range fromabout 50 KHz to 13.56 MHz to produce up to 3000 W. In one embodiment,the source 131 (i.e., the RF generator 134 and matching network 135) andthe process chamber 102 are coupled to the same ground terminal 184,such as the sidewall 158. The ground terminal 184 may further beelectrically coupled (i.e., short-circuited) to a common groundreference of a semiconductor substrate processing system, whichencompasses the reactor 100.

The showerhead 120 and the substrate pedestal 126 together form a pairof spaced apart electrodes. When RF power is applied to either one ofsuch electrodes while the other one is coupled to the ground terminal184 (e.g., the sidewall 158), gas in the reaction volume 154 is ignitedinto a plasma. When no RF power is provided to the showerhead 120 andthe substrate pedestal 126, the reactor 100 is configured to perform aCVD process. For example, to perform a PECVD process, the RF power maybe applied to the showerhead 120, while the substrate pedestal 126 iscoupled to the ground terminal 184. During the PECVD process, a groundreference 183 of the source 131 and the ground terminal 184 of theprocess chamber 102 (e.g., sidewall 158) are coupled together.

To facilitate the cleaning process, the process chamber 102 furthercomprises a switch 180. A common contact (i.e., contact C) of the switch180 is coupled to the showerhead 120, while one of selectable contacts(e.g., contact A) is coupled to the lid 112 and the other selectablecontact (e.g., contact B) is coupled to the ground terminal 184.

In one embodiment, the source 131 applies RF power to the lid 112, whilethe lid 112 is electrically coupled to the blocking plate 164. In thisembodiment, the showerhead 120 is electrically isolated within thesecond portion 105 (i.e., from the blocking plate 164 and lid 112) andfrom the first portion 103 using, e.g., isolators 174 and 176,respectively. Further, the sidewall 158 and, optionally, the substratepedestal 126, are electrically coupled to the connected together groundreference 183 and ground terminal 184.

The isolators 174 and 176 may be conventionally formed, e.g., from atleast one dielectric material such as alumina (Al₂O₃), polyimide, andthe like. The isolators 174 and 176 are also formed such that vacuumperformance of the process chamber 102 is maintained, e.g., eachisolator may be adapted to O-ring or other seal generally used in avacuumed vessel, such as the process chamber 102, to vacuumize theinterior of the vessel.

The switch 180 is generally a double-throw switch. Those skilled in theart will appreciate, that such connections may be performed using, e.g.,two single-throw switches and the like. When the switch 180 is set to afirst position SW1, the switch provides a short circuit between the lid112 (contact A) and the showerhead 120 (contact C). Similarly, when theswitch 180 is set to a second position SW2, the switch provides a shortcircuit between the showerhead 120 (contact C) and the ground terminal184 (contact B). As such, when the sidewall 158 is formed from aconductive material, e.g., aluminum, the second position SW2 alsocorresponds to a short circuit between the showerhead 120 and thesidewall 158.

For better performance, connections to contacts A, B, and C are providedusing conductors (e.g., wires, coaxial cables, and the like) of minimalimpedance and length. In one further embodiment, the switch 180 maycomprise more than one set of contacts such as contacts A, B, and C toenhance the operation of the switch (e.g., reduce contact resistancebetween contacts C and A in the first position SW1 or between contactsor C and B the a second position SW2).

The switch 180 may be operated manually or, alternatively, by anactuator 182 (e.g., a solenoid, linear motor, and the like), controlled,e.g., by the controller 110. In the depicted embodiment, the controller110, using the actuator 182, may set the switch 180 to the firstposition SW1, to the second position SW2, or trigger the switch from onesuch position to another.

When the switch 180 is set to the first position SW1, the processchamber 102 is configured for performing a CVD or PECVD process. Duringsuch process, the process gas is supplied into the chamber. When theprocess chamber 102 performs a CVD process, no RF power is applied tothe process chamber 102 (i.e., to the lid 112 and, respectively, to theshowerhead 120). As such, during the CVD process, no plasma is developedin the chamber 102. Alternatively, when the process chamber 102 performsa PECVD process, the source 131 applies RF power to lid 112 (coupledfurther to the blocking plate 164) and the showerhead 120, and, as such,energizes the process gas to a plasma in the reaction volume 154.

When the switch 180 is set to the second position SW2, the processchamber 102 is configured for performing a cleaning process. During thecleaning process, cleaning gas is delivered into the chamber. When thecleaning process is performed, the source 131 applies RF power to thelid 112 (coupled further to the blocking plate 164), while theshowerhead 120 is isolated from the lid and coupled to the groundterminal 184. In this configuration, the lid 112 (together with theblocking plate 164) and the showerhead 120 form a pair of spaced apartelectrodes. When the source 131 applies RF power to such electrodes, thecleaning gas is energized to a plasma in the gas mixing plenum 152,however, no gas is energized to a plasma in the reaction volume 154.

In one alternative embodiment (not shown), an isolator may be installedto isolate the lid 112 from the blocking plate 164. In this embodiment,the showerhead 120 is electrically coupled to the blocking plate 164,while the isolator 176 isolates the showerhead 120 from the firstportion 103. During the PECVD process (i.e., when the switch 180 is setto the first position SW1 and the source 131 applies RF power to the lid112), the process gas may be energized to a plasma in the reactionvolume 154, as discussed above in reference to FIG. 1. During thecleaning process (i.e., when the switch 180 is set to the secondposition SW2), the source 131 may energize the cleaning gas to a plasmawithin the first mixing plenum 162 using the blocking plate 164 as theelectrode, while no gas is energized to the plasma in the reactionvolume 154 or gas mixing plenum 152.

The process chamber 102 also comprises conventional systems forretaining and releasing the wafer 128, detection of an end of a process,internal diagnostics, and the like. Such systems are collectivelydepicted in FIG. 1 as support systems 107.

The controller 110 comprises a central processing unit (CPU) 124, amemory 116, and a support circuit 114. The CPU 124 may be of any form ofa general purpose computer processor that can be used in an industrialsetting. The software routines can be stored in the memory 116, such asrandom access memory, read only memory, floppy or hard disk drive, orother form of digital storage. The support circuit 114 is conventionallycoupled to the CPU 124 and may comprise cache, clock circuits,input/output sub-systems, power supplies, and the like.

The software routines, when executed by the CPU 124, transform the CPUinto a specific purpose computer (controller) 110 that controls thereactor 100 such that the processes are performed in accordance with thepresent invention. The software routines may also be stored and/orexecuted by a second controller (not shown) that is located remotelyfrom the reactor 100.

FIG. 2 depicts a flow diagram of an exemplary embodiment of theinventive method of cleaning the chamber 102 as a method 200. Generally,the method 200 is performed after the process chamber 102 hasaccumulated post-CVD deposits that should be removed before furtherprocessing may be performed in the chamber.

The method 200 starts at step 202 and ends at step 218.

At step 204, a CVD (or PECVD) process is terminated in the chamber 102.Step 204 terminates supplying power from the source 131 (PECVD process)and from the heater power supply 106. Alternatively, the heater powersupply 106 may continue applying power during the following cleaningprocess to maintain the substrate pedestal 126 at a predeterminedtemperature. Further, step 204 stops supplying the process gas and thebackside gas (e.g., helium). When pressure of the backside gas behindthe wafer 128 becomes approximately equal to the gas pressure in theprocess chamber 102, step 204 releases the wafer 128 from the supportpedestal 126 and removes the wafer out of the process chamber 102. Step204 uses pump 104 to evacuate any traces of the process gas from theprocess chamber 102 and, as such, establishes vacuum in the chamber.During step 204, the switch 180 is set to the first position SW1,corresponding to a short circuit between the lid 112 and the showerhead120 (described in reference to FIG. 1 above).

At step 206, the switch 180 is set to the second position SW2,corresponding to a short circuit between the showerhead 120 and theground terminal 184, as described above in reference to FIG. 1.

At step 208, the cleaning gas is supplied, e.g., via the inlet port 160,into the process chamber 102 from the gas panel 108. In one embodiment,the cleaning gas comprises at least one gas such as nitrogen trifluoride(NF₃) and a carrier gas such as at least one of helium (He), argon (Ar)and the like. Other cleaning gases may comprise fluorine (F₂), sulfurhexafluoride (SF₆), fluorocarbons (e.g., C₂F₆, C₂F₄, and the like),carbon tetrachloride (CCl₄), hexachlorocarbide (C₂Cl₆), and the like. Inone alternative embodiment, step 206 additionally applies power from theheater power supply 106 to the resistive heater 130 (or an optionalsource of radiant heat).

In one exemplary embodiment, step 208 supplies nitrogen trifluoride at aflow rate of about 500 to 6000 sccm, as well as helium at a flow rate ofabout 0 to 3000 sccm (i.e., a NF₃:He flow ratio ranging from 1:0 to1:6). Step 208 also maintains gas pressure in the process chamber 102between 1 and 6 torr and temperature of the support pedestal 126 between200 and 450 degrees Celsius. One specific recipe supplies approximately750 sccm of NF₃ and 500 sccm of He (i.e., a NF₃:He flow ratio of about1:0.7), and maintains gas pressure at about 1.6 torr and temperature ofthe support pedestal at about 350 degrees Celsius.

In one alternative embodiment, step 208 may be performed before step206. Further, steps 206 and 208 may be performed contemporaneously.

At step 210, the source 131 supplies RF power to the lid 112, thusenergizing the cleaning gas to a plasma within the gas mixing plenum152. The plasma dissociates the cleaning gas and produces free radicalsand ionic species that can effectively transform the post-CVD residue involatile compounds. At the same time, the free radicals and ionicspecies are chemically almost inert towards the materials (e.g.,aluminum) used to form internal parts of the chamber 102 (e.g., thesubstrate pedestal 126, lining 113, and the like). A mixture of the freeradicals and ionic species is further dispersed by the showerhead 120into the reaction volume 154. From the reaction volume 154, the mixturepropagates into other areas of the process chamber 102 and removes thepost-CVD residue therein. A portion of the mixture also migrates intothe first mixing plenum 162 and removes the residue from surfaces of theplenum.

The plasma of the cleaning gas is struck in close proximity to theshowerhead 120, and, as such, recombination of the free radicals andionic species in the reaction volume 154 is minimal. Specifically, therecombination is minimal in the apertures 172 and 168, as well as withinthe entire internal volume of the process chamber 102. The recombinationof the free radicals and ionic species may further be reduced bycontrolling the power and frequency of the source 131. A level of RFpower generally depends upon the thickness of accumulated post-CVDresidue (deposits), chemistry of the cleaning gas, a predeterminedduration of the cleaning process, a showerhead design, and the like.Similarly, the frequency of the applied RF power may depend on thechemical composition of the deposits and chemistry of the cleaning gas.In the exemplary embodiment discussed above, step 210 applies about 500to 2500 W of RF power at 13.56 MHz, while one specific recipe applies1000 W.

At step 212, the cleaning process is performed in the process chamber102. During step 212, reactive components of the cleaning gas (i.e.,free radicals and ionic species) etch the post-CVD deposits andtransform the deposits into volatile compounds. The volatile compoundsare then evacuated from the chamber through the exhaust port 186 usingthe vacuum pump 104. A duration of step 212 continues until the depositsare removed from internal parts of the process chamber 102.

In one exemplary application, the inventive method is used to clean theCVD chamber after a layer of low-k (i.e., low dielectric constant)dielectric material, such as, e.g., carbon doped silicon oxide, has beendeposited upon about 2400 wafers. The carbon doped silicon oxide may bedeposited by methods known in the art, such as methods disclosed incommonly assigned U.S. patent application Ser. No. 09/820,463, filedMar. 28, 2001, which is incorporated herein by reference. In theexemplary embodiment when cleaning gas comprises nitrogen trifluorideand helium, a duration of the cleaning process of step 212 is between 2and 6 minutes. In this application, the etch rate during the cleaningprocess is between about 120 and 250 Angstroms/sec, while the RF powerfrom the source 131 is controlled in a range from about 500 to 1500 W.In one embodiment, the etch rate was about 195 Angstroms/sec at 1000 W.

The invention substantially improved performance of a conventionalcleaning process. Using the invention, the service interval (i.e., anumber of wafers processed in the process chamber between twoconsecutive cleaning processes) was increased for this application fromabout 2,400 wafers to approximately 10,000 wafers. As such, theinvention improved throughput and productivity of the CVD chamber.

In an alternative embodiment, during step 212, the cleaning gas and RFpower may be provided intermittently. In this embodiment, the cleaninggas and RF power are provided (i.e., active) during a first period oftime and turned off (i.e., inactive) during a second period of time. Assuch, during the fist period, the cleaning process etches the deposits,transforms deposits into volatile compounds, and evacuates suchcompounds from the process chamber. Then, during the second period, thecleaning process restores vacuum in the process chamber. Such cycles ofetching the post-CVD deposits and vacuum restoration are repeated untilthe deposits are removed from internal parts of the chamber. Generally,a duration of the first period is between 2 and 6 minutes, while thesecond period has a duration between 0 and 6 minutes. In one embodiment,the cleaning gas and RF power are provided for about 4 minutes, and theninterrupted for approximately 4 minutes, i.e., the cleaning gas and RFpower are active, together, with a duty cycle of about 50%.

At step 214, the cleaning process is terminated. Specifically, step 214stops applying RF power from the source 131, as well as stops supplyingthe cleaning gas into the process chamber 102. As such, step 214terminates plasma of the cleaning gas in the gas mixing plenum 152 andrestores vacuum in the chamber. The heater power supply 106 may continueapplying power to the resistive heater 130 to maintain the substratepedestal 126 at a predetermined temperature, or may be shut off.

At step 216, the switch 180 is returned to the first position SW1.Similar to steps 206 and 208, in an alternative embodiment, steps 214and 216 may be performed contemporaneously. At step 218, the method 200ends.

FIG. 3 presents a table summarizing parameters through which one canpractice the invention using the reactor of FIG. 1. The parameters forthe embodiment of the invention presented above are summarized in FIG.3. The process ranges and exemplary process data are also presented inFIG. 3. It should be understood, however, that the use of a differentCVD reactor or CVD process may necessitate different process parametervalues and ranges.

Although the forgoing discussion referred to cleaning of a CVD chamber,other process chamber can benefit from the invention. The invention canbe practiced in other semiconductor processing systems wherein theprocessing parameters may be adjusted to achieve acceptablecharacteristics by those skilled in the art by utilizing the teachingsdisclosed herein without departing from the spirit of the invention.

While foregoing is directed to the illustrative embodiment of thepresent invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

1. A semiconductor substrate processing system comprising a chamber forprocessing a substrate, said chamber comprises: a first portioncomprising a substrate support pedestal; a second portion comprising ablocking plate electrode and a source of radio-frequency power; ashowerhead electrode electrically isolated from the first portion andthe second portion; and a switch that couples the showerhead electrodeto the first portion or the second portion, wherein the switch couplesthe showerhead electrode to the first portion during plasma cleaning thechamber.
 2. A semiconductor substrate processing system comprising achamber for processing a substrate, said chamber comprises: a firstportion comprising a substrate support pedestal; a second portioncomprising a blocking plate electrode and a source of radio-frequencypower; a showerhead electrode electrically isolated from the firstportion and the second portion; and a switch that couples the showerheadelectrode to the first portion or the second portion, wherein the switchis a double-throw switch having a common terminal coupled to theshowerhead electrode and selectable terminals coupled to the firstportion and the second portion, respectively.